Moved all of the vessel parsing code into the new RelayDatabase, which
watches some events to dirty the cache when states change. Also modules
will no longer offer to transmit if their part is dead or deactivated.

AntennaRange.cfg: Added isAntenna to the part prefab for all parts with ModuleLimitedDataTransmitters.

AntennaRelay.cs: Added a timer to prevent antennas from re-searching their nearest relay multiple times in a single transmission attempt.

Extensions.cs: Remove IsAntenna stuff because we want that to work without persistence data. Doesn't work yet.

ModuleLimitedDataTransmitter.cs:
* Changed DataRate to return a very tiny number if the antenna cannot transmit.
* Changed the transmission message to indictor if it is using a relay or not.
* Removed IsAntenna in favor of using the prefab... hopefully.